Edited1H magnetic resonance spectroscopy in vivo: Methods and metabolites

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Abstract

The Proton magnetic resonance (1 H-MRS) spectrum contains information about the concentration of tissue metabolites within a predefined region of interest (a voxel). The conventional spectrum in some cases obscures information about less abundant metabolites due to limited separation and complex splitting of the metabolite peaks. One method to detect these metabolites is to reduce the complexity of the spectrum using editing. This review provides an overview of the one-dimensional editing methods available to interrogate these obscured metabolite peaks. These methods include sequence optimizations, echo-time averaging, J-difference editing methods (single BASING, dual BASING, and MEGA-PRESS), constant-time PRESS, and multiple quantum filtering. It then provides an overview of the brain metabolites whose detection can benefit from one or more of these editing approaches, including ascorbic acid, γ-aminobutyric acid, lactate, aspartate, N-acetyl aspartyl glutamate, 2-hydroxyglutarate, glutathione, glutamate, glycine, and serine. Magn Reson Med 77:1377-1389, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

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The Role of GABA in Human Motor Learning

Charlotte Stagg, Velicia Bachtiar, Heidi Johansen-Berg (2011)

Results There is considerable variability in motor learning behavior across individuals [7], and the present study aimed to test whether some of this variability could be explained by variation in responsiveness of the GABA system, because GABA modulation plays an important role in learning [1–4]. As a measure of GABA responsiveness, we used magnetic resonance spectroscopy (MRS) to quantify changes in GABA concentration following anodal transcranial direct current stimulation (tDCS), a noninvasive technique that decreases GABA within the motor cortex [5], increases cortical excitability [8], and enhances short-term learning [9]. We predicted that individuals who show less tDCS-mediated GABA modulation would show less behavioral evidence of motor learning and less modulation of fMRI responses during learning. Subjects participated in three experimental sessions on different days. The first two sessions were MRS sessions, during which GABA-edited spectra were acquired before and after 10 min of tDCS. In the third session, subjects performed an explicit sequence learning task during fMRI, and no tDCS was applied. Motor Behavior Motor learning was assessed via change in reaction times to a visually cued explicit sequence learning task performed with the four fingers of the right hand during fMRI acquisition in session 3. All subjects showed a significant reduction in reaction times across successive learning blocks (Figure 1A; repeated-measures analysis of variance, main effect of BLOCK F(15,150) = 19.95; p 2.0 and a (corrected) cluster significance threshold of p = 0.01.

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Current practice in the use of MEGA-PRESS spectroscopy for the detection of GABA.

Andrew McGonigle, Nicolaas A. J. Puts, Paul Mullins … (2014)

There is increasing interest in the use of edited proton magnetic resonance spectroscopy for the detection of GABA in the human brain. At a recent meeting held at Cardiff University, a number of spectroscopy groups met to discuss the acquisition, analysis and interpretation of GABA-edited MR spectra. This paper aims to set out the issues discussed at this meeting, reporting areas of consensus around parameters and procedures in the field and highlighting those areas where differences remain. It is hoped that this paper can fulfill two needs, providing a summary of the current 'state-of-the-art' in the field of GABA-edited MRS at 3T using MEGA-PRESS and a basic guide to help researchers new to the field to avoid some of the pitfalls inherent in the acquisition and processing of edited MRS for GABA. Copyright © 2012 Elsevier Inc. All rights reserved.

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Resting GABA concentration predicts peak gamma frequency and fMRI amplitude in response to visual stimulation in humans.

Suresh D. Muthukumaraswamy, Richard A. E. Edden, Derek K Jones … (2009)

Functional imaging of the human brain is an increasingly important technique for clinical and cognitive neuroscience research, with functional MRI (fMRI) of the blood oxygen level-dependent (BOLD) response and electroencephalography or magnetoencephalography (MEG) recordings of neural oscillations being 2 of the most popular approaches. However, the neural and physiological mechanisms that generate these responses are only partially understood and sources of interparticipant variability in these measures are rarely investigated. Here, we test the hypothesis that the properties of these neuroimaging metrics are related to individual levels of cortical inhibition by combining magnetic resonance spectroscopy to quantify resting GABA concentration in the visual cortex, MEG to measure stimulus-induced visual gamma oscillations and fMRI to measure the BOLD response to a simple visual grating stimulus. Our results demonstrate that across individuals gamma oscillation frequency is positively correlated with resting GABA concentration in visual cortex (R = 0.68; P < 0.02), BOLD magnitude is inversely correlated with resting GABA (R = -0.64; P < 0.05) and that gamma oscillation frequency is strongly inversely correlated with the magnitude of the BOLD response (R = -0.88; P < 0.001). Our results are therefore supportive of recent theories suggesting that these functional neuroimaging metrics are dependent on the excitation/inhibition balance in an individual's cortex and have important implications for the interpretation of functional imaging results, particularly when making between-group comparisons in clinical research.

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Author and article information

Journal

Title: Magnetic Resonance in Medicine

Abbreviated Title: Magn. Reson. Med.

Publisher: Wiley

ISSN: 07403194

Publication date Created: April 2017

Publication date (Print): April 2017

Publication date (Electronic): February 02 2017

Volume: 77

Issue: 4

Pages: 1377-1389

Affiliations

[1 ]Department of Radiology; University of Calgary; Calgary AB T2N 1N4 Canada

[2 ]Child and Adolescent Imaging Research (CAIR) Program, Alberta Children's Hospital Research Institute; University of Calgary; Calgary AB T3B 6A9 Canada

[3 ]Hotchkiss Brain Institute; University of Calgary; Calgary AB T2N 1N4 Canada

[4 ]Russell H. Morgan Department of Radiology and Radiological Science; The Johns Hopkins University School of Medicine; Baltimore MD 21205 USA

[5 ]F.M. Kirby Center for Functional Brain Imaging, Kennedy Krieger Institute; Baltimore MD 21205 USA.